Use the Async versions of SCCudaMemcpy* to improve gpu performance.

Improves gpu performance by removing unnecessary synchronizing with the host.

Here are a couple of traces from the nvidia profiler that show the gaps in between dmas and processing in the synchronous and aysncronous cases:

![cuda_synchronous](https://f.cloud.github.com/assets/5377197/1084620/79919da0-15b2-11e3-932e-7067c688a491.jpg)

![cuda_async](https://f.cloud.github.com/assets/5377197/1084637/af2f9688-15b2-11e3-8165-c247db5c5e27.jpg)